Hall mobility and its relationship to the persistent photoconductivity of undoped GaN

Abstract

Temperature-variable Hall effect measurements have been used to investigate the electrical properties of undoped GaN, which has electron densities in the order of mid-1016 cm-3 and the Hall mobility varying from 500 cm2/sV. We found that very strong ionized impurity scattering limits the Hall mobility of GaN. Illumination even at 77 K has very little effect on the electron density but can lead to a noticeable persistent increase of the Hall mobility. The induced persistent photoconductivity (PPC) effect is, therefore, related to the Hall mobility through intrinsic electrically active defects. The properties of those defects were further investigated by monitoring the transient change of resistivity after removal of illumination at different temperatures. We have found that the recapturing process of excited electrons into illumination-neutralized defects is the mechanism responsible for the PPC effect of undoped GaN.